What is spinal muscular atrophy (SMA)?

Updated: Apr 28, 2014
  • Author: Hidehiro Takei, MD; Chief Editor: Adekunle M Adesina, MD, PhD  more...
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SMA comprises a large group of genetically determined neuromuscular disorders that are characterized by progressive degeneration of spinal LMNs (ie, alpha motor neurons in the anterior horns) accompanied by amyotrophy, with no evidence of sensory or pyramidal tract involvement. This condition is genetically heterogeneous, with autosomal recessive (most common), autosomal dominant, and X-linked recessive modes of inheritance.

The International SMA Consortium defined the following 4 clinical groups, depending on the age of onset and achieved motor abilities [3] :

  • Type I SMA (acute form, Werdnig-Hoffmann disease)

  • Type II SMA (intermediate form)

  • Type III SMA (juvenile form, Kugelberg-Welander disease)

  • Type IV SMA (adult form)

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